SMA affects approximately 1 in 10,000 babies, and nearly 1 in every 50 Americans is a genetic carrier. A defect in the survival motor neuron gene 1 (SMN1) causes SMA. When functioning normally, this gene produces a protein critical to the function of nerves that control the body’s muscles. When this gene is missing or defective, those nerve cells slowly die, leading to debilitating and sometimes life-threatening muscle weakness.

Children have muscle weakness or wasting more severe in the trunk and upper legs and arms than in the muscles of the hands and feet. They may also have difficulty performing the basic life functions, such as breathing and swallowing. However, spinal muscular atrophy does not affect their ability to think, learn, feel, and relate to others.

What are the symptoms of spinal muscular atrophy?

There are three types of spinal muscular atrophy based on ages of onset, severity, and progression.

SMA type I is evident by the time a child is 6 months old. Symptoms are:

diminished tendon reflexes

fasciculations (brief muscle contractions causing a flicker of movement under the skin)

hypotonia (severely reduced muscle tone)

impaired breathing

restricted movement of the limbs

scoliosis (curvature of the spine) or other spinal deformities

swallowing and feeding difficulty

tremors

Children with SMA type I never sit or stand, and many do not live past age 2. However, the survival rate for SMA type I children has increased in recent years thanks to more advanced clinical care.

Progression of SMA type II varies. Though overall life expectancy is lowered, many patients live into adolescence or young adulthood.

SMA type III is the least severe form and affects children ages 2 to 17 years old. Symptoms are:

abnormal gait

difficulty running, climbing steps, or rising from a chair

fine tremor of the fingers

higher risk of respiratory infections

joint contractures, the chronic shortening of muscles or tendons around joints caused by abnormal muscle tone and weakness

scoliosis

Individuals with SMA type III may have a normal lifespan.

In addition, there is one other rare form of this condition called congenital SMA with arthrogryposis (persistent contracture of joints with fixed abnormal position of the limbs). Symptoms are:

chest deformity

drooping of the upper eyelids

respiratory problems

scoliosis

severe contractures

unusually small jaws

How is spinal muscular atrophy diagnosed?

At the Pediatric SMA Clinical Research Center, a neurologist with special expertise in SMA and pediatric neuromuscular disease will provide a comprehensive evaluation of your child.

A thorough neurological exam will be conducted and any previous tests reviewed. The following diagnostic tools may then be recommended:

Blood Test. This shows if there are deletions or mutations of the SMN1 gene. Genetic testing identifies at least 95 percent of SMA Types I, II, and III.

Electromyography. This test records the electrical activity from the brain and/or spinal cord to a peripheral nerve root that controls muscle function in the arms and legs

Nerve Conduction Velocity Studies. These tests measure electrical energy by assessing the nerve’s ability to send a signal to the muscles.

Muscle biopsy. A small needle is insert into the muscle and a sample is taken. This test is used to diagnose neuromuscular disorders and may also reveal if a child is a carrier of a defective gene.

What is the treatment for spinal muscular atrophy?

Our Spinal Muscular Atrophy Clinic and research network provide state-of-the-art care to children with this disorder and offer them the opportunity to participate in clinical trials assessing the latest treatments.

Our team has special expertise in SMA and other neuromuscular disorders and collaborates with cardiologists, neurologists, nurse practitioners, orthopedists, physiatrists, psychologists, pulmonologists, and therapists. Treatments may include:

assisted ventilation as needed during daytime

assistive devices such as supports or braces, orthotics, speech synthesizers, and wheelchairs

behavioral counseling and antidepressants, as necessary

injections of botulinum toxin in salivary glands to treat jaw spasms or drooling